School bus crossing arms are designed to extend to a perpendicular position relative to a front bus bumper when a school bus stops to pick up or discharge passengers. In this perpendicular position, such a crossing arm will block arriving and departing passengers from crossing immediately in front of a school bus and below the bus driver's field of vision. U.S. Pat. No. 5,357,239, granted to me Oct. 18, 1994, shows such a crossing arm assembly, or "safety gate," that comprises a hollow or solid bar attached at one end to a plastic bracket. The plastic bracket is configured to pivotally mount the bar on a housing.
Others have attempted to provide improved crossing arm arrangements. For instance, U.S. Pat. No. 4,697,541 granted Oct. 6, 1987 to James H. Wicker discloses a crossing arm unit that comprises a short pivot plate. The pivot plate is made of a sturdy, relatively heavy gage metal (e.g. 3.5 in. of 14-gauge steel), a longer support plate of relatively light gauge metal (e.g. 20 in. of 0.08-in. aluminum plate) and a long U-shaped rod (e.g. 4 ft. of 1/4-in. aluminum rod). The U-shaped rod serves as a pedestrian barrier. According to the Wicker patent specification the crossing arm unit is light in weight to avoid structural problems with its support. The unit is easily supported, is simple to construct and is economical to manufacture. The Wicker patent, at column 1, also states that crossing arms have been made of lightweight fiber glass rods and that the Wicker construction improves on these prior art constructions.
However, the Wicker construction is unduly complicated particularly when its assembly requirements are taken into account. Moreover, the long U-shaped rod is fragile, deforms easily and is prone to plastic rather than elastic deformation. The U-shaped rod also requires a strut that further complicates and adds to the expense of the Wicker construction. Furthermore, the U-shaped rod has a narrow profile and is not highly visible.
U.S. Pat. No. 5,199,754 granted Apr. 6, 1993 to Lowell J. D. Freeman discloses a crossing arm or barrier whose construction includes tubular fiberglass. While the Freeman crossing arm construction is simple in comparison to the Wicker construction, it includes only a single rod that is heavy and rigid.
U.S. Pat. No. 3,153,398, granted Oct. 20, 1964 to George LaVerne Runkle and Gilbert S. Sheets, discloses a crossing arm structure that comprises a channel-shaped section of light sheet metal. The channel-shaped section is stiffened by a U-section having out-turned legs fixed to the back of the channel shaped section. The crossing arm assembly is shaped to fit in a recess in the front bumper of a bus. The assembly also includes a rubber guard structure that has a hollow rectangular center portion that is cemented to the channel section and flange portions that seal off the bumper recess.
This crossing arm structure is unduly complicated and expensive to manufacture. Furthermore the arrangement requires a hinge structure to attach the crossing arm to the bumper. This hinge structure further complicates construction and adds expense.
All the above designs have crossing arms that are cantilevered, i.e., supported by and extending rigidly from only one end. Therefore, a person applying force near the free distal end of any of these arms has a tremendous mechanical advantage over the mechanisms associated with the support and can damage the support or permanently bend or break the arm. If not securely latched to the front of the bus, the inertia of the arm can cause it to swing forward from the bus, uncommanded, whenever the bus decelerates. In addition, an arm supported in this manner is prone to sagging under its own weight. Arm weight can also make it difficult to dampen oscillations that occur when arm rotation is stopped abruptly in the perpendicular extended position.
Therefore, what is needed is a crossing arm that is less massive and therefore has less momentum to cause it to swing forward whenever its host bus stops or slows in traffic. What is also needed is a crossing arm that resists sagging, is configured to withstand considerable abuse, e.g., hinge damage that can result when force is applied along the length of the arm, and is economical to manufacture.